1. Field of the Invention
The present invention relates to an inkjet printhead. More particularly, the present invention relates to a bubble-jet ink-jet printhead, a manufacturing method thereof, and a method of ejecting ink.
2. Description of the Related Art
The ink ejection mechanisms of an ink-jet printer are largely categorized into two types: an electro-thermal transducer type (bubble-jet type) in which a heat source is employed to form a bubble in ink causing ink droplets to be ejected, and an electromechanical transducer type in which a piezoelectric crystal bends to change the volume of ink causing ink droplets to be expelled.
With reference to FIGS. 1A and 1B, a conventional bubblejet type ink ejection mechanism will now be described. When a current pulse is applied to a first heater 12 consisting of resistive heating elements formed in an ink channel 10 where a nozzle 11 is located, heat generated by the first heater 12 boils ink 14 to form a bubble 15 within the ink channel 10, which causes an ink droplet 14xe2x80x2 to be ejected.
To be useful, an ink-jet printhead having this bubble-jet type ink ejector must meet the following conditions. First, it must have a simplified manufacturing process, i.e., a low manufacturing cost and a high volume of production must be possible. Second, to produce high quality color images, creation of minute satellite droplets that trail ejected main droplets must be prevented. Third, when ink is ejected from one nozzle, or ink refills an ink chamber after ink ejection, cross-talk between an adjacent nozzles from which no ink is ejected must be prevented. To this end, a back flow of ink in the opposite direction of a nozzle must be avoided during ink ejection. Another heater 13 shown in FIGS. 1A and 1B is provided for this purpose. This second heater 13 is similarly capable of forming a bubble 16. Fourth, for a high speed print, a cycle beginning with ink ejection and ending with ink refill must be as short as possible.
However, the above conditions tend to conflict with one another, and furthermore, the performance of an ink-jet printhead is closely associated with structures of an ink chamber, an ink channel, and a heater, the type of formation and expansion of bubbles, and the relative size of each component.
In efforts to overcome problems related to the above requirements, ink-jet printheads having a variety of structures have been proposed in, for example, U.S. Pat. Nos. 4,339,762; 4,882,595; 5,760,804; 4,847,630; and 5,850,241; European Patent No. 317,171, and an article by Fan-Gang Tseng, Chang-Jin Kim, and Chih-Ming Ho entitled, xe2x80x9cA Novel Microinjector with Virtual Chamber Neckxe2x80x9d, IEEE MEMS ""98, pp. 57-62. However, the ink-jet printheads proposed in the above patents or literature may satisfy some of the aforementioned requirements but do not completely provide an improved ink-jet printing approach.
It is a feature of an embodiment of the present invention to provide a bubble-jet type ink-jet printhead having a structure that satisfies the above-mentioned requirements.
It is another feature of an embodiment of the present invention to provide a method of manufacturing the bubble-jet type ink-jet printhead having a structure that satisfies the above-mentioned requirements.
It is a further feature of an embodiment of the present invention to provide a method of ejecting ink in a bubble-jet type ink printhead.
In order to provide the first feature, an embodiment of the present invention provides an ink-jet printhead including a substrate having an ink supply manifold, an ink chamber, and an ink channel, a nozzle plate having a nozzle, and a heater consisting of resistive heating elements, and an electrode for applying current to the heater. The manifold supplying ink, the ink chamber filled with ink to be ejected, and the ink chamber for supplying ink from the manifold to the ink chamber are integrally formed on the substrate. The nozzle plate is stacked on the substrate, wherein the nozzle plate has the nozzle at a location corresponding to the central part of the ink chamber. The heater is formed in an annular shape on the nozzle plate and centered around the nozzle of the nozzle plate. The ink chamber is substantially hemispherical. The ink channel further includes a bubble barrier for reducing the diameter of the ink channel prior to the ink chamber.
In a preferred embodiment, a bubble guide and a droplet guide, both of which extend down the edges of the nozzle in the depth direction of the ink chamber are formed to guide the direction in which a bubble grows and the shape of the bubble, and the ejection direction of an ink droplet during ink ejection, respectively. The heater is formed in the shape of a horseshoe so that the bubble has a substantially doughnut shape.
In order to provide the second feature, an embodiment of the present invention provides a method of manufacturing a bubble-jet type ink-jet printhead, in which a substrate is etched to form an ink chamber, an ink channel, and ink supply manifold thereon. A nozzle plate is formed on the surface of the substrate, and an annular heater is formed on the nozzle plate. The substrate is etched to form the ink supply manifold. Furthermore, electrodes for applying current to the annular heater are formed. A nozzle plate is etched to form a nozzle having a diameter less than the annular heater on the inside of the annular heater. The substrate exposed by the nozzle is etched to form the substantially hemispherical ink chamber having a diameter greater than the annular heater. The substrate is etched from the surface to form the ink channel for connecting the ink chamber with the manifold.
In a preferred embodiment, the ink chamber is formed by anisotropically etching the substrate exposed by the nozzle to a predetermined depth, and isotropically etching the substrate, so that it has a hemispherical shape.
In a preferred embodiment, in order to form the ink channel, the nozzle plate is etched from the outside of the annular heater toward the manifold to form a groove for exposing the substrate at the same time that a nozzle plate is etched to form the nozzle. Then, the substrate exposed by the groove is etched at the same time that the substrate is isotropically etched for forming the ink chamber.
In a preferred embodiment, in order to form the ink chamber, the substrate exposed by the nozzle is etched to a predetermined depth to form a trench. Then, a predetermined material layer is deposited over the anisotropically etched substrate to a predetermined thickness and the material layer is anisotropically etched to expose the bottom of the trench and form a spacer of the material layer along the sidewalls of the trench. Then, the substrate exposed to the bottom of the trench is isotropically etched.
In order to provide the third feature, an embodiment of the present invention provides a method of ejecting ink in a bubble-jet type ink-jet printhead. According to the ejection method, a bubble having a substantially doughnut shape, the center portion of which opposes the nozzle, is formed within the ink chamber filled with ink. The doughnut-shaped bubble expands and coalesces under the nozzle to cut off the tail of an ejected ink droplet.
According to an embodiment of the present invention, a bubble is formed in a doughnut shape, which satisfies the above requirements for ink ejection. Furthermore, this embodiment allows a simple manufacturing process and high volume production of printheads in chips.
These and other features and advantages of the embodiments of the present invention will be readily apparent to those of ordinary skill in the art upon review of the detailed description that follows.